For example, the joke about the Chinese restaurant ("I'd be more concerned about what they're passing off as chicken") plays off of the stereotype that Chinese people eat dogs and cats, and the “passing off” remark implies that the Chinese restaurant owners are deceptive and would immorally and illegally serve their guests a different kind of meat than advertised. I can definitely see how that joke would be considered offensive.
The author labels that joke as "harmless" but you don't have to be a Chinese censor to interpret it as reinforcing harmful stereotypes. I dare you to show that scene at a liberal college and notice how few laughs you get.
Similarly, the racist remarks about Chinese people made by Sheldon's mom are somewhat offensive if taken at face value. I guess the joke is supposed to be at her expense instead ("old people are racists" is an American comedy cliche, if a somewhat tired one) but it's conceivable that either the censors didn't get that, or they feared that their audience didn't get that, so they decided to cut it out entirely.
"They wouldn't get that" is probably also the right explanation for censoring the joke about Jews eating at Chinese restaurants during Christmas, which is a very American tradition. That doesn't imply the joke needs to go, but I can see how that would, at best, leave Chinese viewers scratching their heads.
Did you see the recent video where the white guy dressed up in a poncho, big hat, and fake mustache and carried around maracas? He asked a bunch of white kids on a college campus if they thought his outfit was offensive to Mexicans, and they all said yes.
Then he went to the Mexican part of town and asked actual Mexicans, and they all said it was funny or that they liked that he was trying to honor their culture. Not one of them was offended.
So perhaps it would be good to ask a Chinese person if this joke offends them.
In many ways the virtue signaling is doing the thing they are accusing others of - using a culture (that isn't theirs) as a weapon for social status.
I felt this pull at university, when I spent a brief time flirting with the art society. everyone there had these kinds of values, and it would have made fitting in significantly easier if I had vocally agreed with them. this would have been especially tempting if I was (more) lonely and desperate for company, as many people are
as it was I mostly just kept quiet or carefully found points of agreement. I suspect if I was the type of person to give in to this zeitgeist, and not particularly question my beliefs, it could easily have developed into something real without any need for narcissistic tendencies